The Astrophysical Journal, 833:195 (9pp), 2016 December 20 doi:10.3847/1538-4357/833/2/195 © 2016. The American Astronomical Society. All rights reserved. THE SXDF-ALMA 2 arcmin2 DEEP SURVEY: STACKING REST-FRAME NEAR-INFRARED SELECTED OBJECTS Wei-Hao Wang1,2, Kotaro Kohno3,4, Bunyo Hatsukade5,20, Hideki Umehata3,6, Itziar Aretxaga7, David Hughes7, Karina I. Caputi8, James S. Dunlop9, Soh Ikarashi8, Daisuke Iono5,10, Rob J. Ivison6,9, Minju Lee5,11, Ryu Makiya12,13, Yuichi Matsuda5,10, Kentaro Motohara3, Kouichiro Nakanish5,10, Kouji Ohta14, Ken-ichi Tadaki15, Yoichi Tamura3, Tadayuki Kodama5,10, Wiphu Rujopakarn12,16, Grant W. Wilson17, Yuki Yamaguchi3, Min S. Yun17, Jean Coupon18, Bau-Ching Hsieh1, and Sébastien Foucaud19 1 Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan 2 Canada–France–Hawaii Telescope (CFHT), 65-1238 Mamalahoa Hwy., Kamuela, HI 96743, USA 3 Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan 4 Research Center for the Early Universe, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan 5 National Astronomical Observatory of Japan (NAOJ), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 6 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany 7 Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Luis Enrique Erro 1, Sta. Ma. Tonantzintla, Puebla, Mexico 8 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700AV Groningen, The Netherlands 9 Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK 10 SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 11 Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 133-0033, Japan 12 Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa, 277-8583 (Kavli IPMU, WPI), Japan 13 Max-Planck-Institut für Astrophysik (MPA), Karl-Schwarzschild Str. 1, D-85741 Garching, Germany 14 Department of Astronomy, Kyoto University, Kyoto 606-8502, Japan 15 Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse, D-85748 Garching, Germany 16 Department of Physics, Faculty of Science, Chulalongkorn University, 254 Phayathai Rd., Pathumwan, Bangkok 10330, Thailand 17 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA 18 Astronomical Observatory of the University of Geneva, ch. d’Ecogia 16, CH-1290 Versoix, Switzerland 19 Center for Astronomy & Astrophysics, Department of Physics & Astronomy, Shanghai JiaoTong University, 800 Dongchuan Rd., Shanghai 200240, China Received 2016 June 26; revised 2016 September 20; accepted 2016 September 27; published 2016 December 16 ABSTRACT We present stacking analyses on our ALMA deep 1.1 mm imaging in the Subaru/XMM-Newton Deep Survey Field using 1.6 and 3.6 μm selected galaxies in the CANDELS WFC3 catalog. We detect a stacked flux of 11 −1 ∼0.03–0.05 mJy, corresponding to LIR < 10 L and a star formation rate (SFR) of ~15 M yr at z=2. We find that galaxies that are brighter in the rest-frame near-infrared tend to also be brighter at 1.1 mm, and galaxies fainter than m3.6m m = 23 do not produce detectable 1.1 mm emission. This suggests a correlation between stellar mass and SFR, but outliers to this correlation are also observed, suggesting strongly boosted star formation or extremely large extinction. We also find tendencies that redder galaxies and galaxies at higher redshifts are brighter at 1.1 mm. Our field contains z ~ 2.5 Hα emitters and a bright single-dish source. However, we do not find evidence of bias in our results caused by the bright source. By combining the fluxes of sources detected by ALMA and fluxes of faint sources detected with stacking, we recover a 1.1 mm surface brightness of up to 20.3±1.2 Jy deg−2, comparable to the extragalactic background light measured by COBE. Based on the fractions of optically faint sources in our and previous ALMA studies and the COBE measurements, we find that approximately half of the cosmic star formation may be obscured by dust and missed by deep optical surveys. Much deeper and wider ALMA imaging is therefore needed to better constrain the obscured cosmic star formation history. Key words: cosmic background radiation – galaxies: evolution – galaxies: high-redshift – submillimeter: galaxies 1. INTRODUCTION and in the FIR from space to detect and study the FIR sources (see Casey et al. 2014 and Lutz 2014 for recent reviews). The extragalactic background light (EBL) is a measure of the radiative energy production from star formation and black hole However, because of the effect of confusion on single-dish telescopes, the vast majority of the detected objects have accretion throughout the history of the universe. It is now 12 known that the optical and far-infrared (FIR) portions of the infrared luminosities well above 10 L, corresponding to the / EBL have comparable integrated strengths (e.g., Dole bright end of the infrared luminosity functions. In the mm – et al. 2006), implying that a large amount of the rest-frame submm, typically only 10% 40% of the EBL is resolved into ( UV radiation is absorbed by dust and reradiated in the FIR. In discrete bright sources by bolometer array cameras e.g., order to understand the star formation history and accretion Barger et al. 1999; Borys et al. 2003; Greve et al. 2004; Wang history fully, it is thus crucial to map the high-redshift dusty et al. 2004; Coppin et al. 2006; Weiß et al. 2009; Scott et al. galaxies that give rise to the FIR EBL. 2010; Hatsukade et al. 2011). In the FIR, Herschel SPIRE Numerous deep imaging surveys have been carried out in the surveys are only able to directly resolve ~15% of the millimeter and submillimeter (mm/submm) from the ground 200–500 μm EBL into bright sources (e.g., Oliver et al. 2010). Imaging surveys in strong lensing clusters can 20 NAOJ Fellow. nearly fully resolve the mm/submm EBL (e.g., Cowie 1 The Astrophysical Journal, 833:195 (9pp), 2016 December 20 Wang et al. et al. 2002; Smail et al. 2002; Knudsen et al. 2008; Chen z ~ 2.5 Hα-selected star-forming galaxies (e.g., Tadaki et al. 2013) and provide valuable insight into the nature of the et al. 2013). The calibration and imaging are performed with faint sources (Chen et al. 2014). However, the sample sizes for the Common Astronomy Software Application package the lensed faint sources remain extremely small. (McMullin et al. 2007). The visibility data were naturally The advent of ALMA is transforming studies of mm/submm weighted to produce a CLEANed map with a synthesized beam sources. ALMA not only provides a powerful means of of 0.53´ 0.41(PA=64°). In this work, we only consider following up the single-dish sources, but also serves as a survey the deep region where the effective coverage is greater than machine. In particular, ALMA has the combination of high 75% of the peak primary beam response, indicated by the angular resolution and high sensitivity, the two key elements contours in Figure 1. This excludes a bright object near the map required to detect faint galaxies beyond the confusion limits of edge (SXDF-ALMA 3 in Yamaguchi et al. 2016). The area in single-dish telescopes. In early ALMA cycles, various small- this region is 1.58 arcmin2 and the typical rms noise is 62 μJy scale continuum surveys have been conducted (e.g., Umehata beam−1. There are 16 sources detected in this area at >4s, and et al. 2015; Dunlop et al. 2016, hereafter D16). However, eight sources at >4.5s. Up to one-third of the >4s sources because of the limited observing time, even these ALMA could be spurious, based on the number of negative peaks surveys did not reach the sensitivity required to fully resolve (H16), and the number of spurious sources decreases to zero the EBL over large areas. Sources detected in these ALMA at >4.7s. surveys typically account for ~40% of the EBL (e.g., ) Hatsukade et al. 2016, hereafter H16; D16 and the majority 2.2. Optical and NIR Data of the dusty galaxies remain undetected. One way to break through the current sensitivity limit is, instead of relying on Our stacking analyses are based on the WFC3 detected contiguous ALMA mosaic surveys, to exploit the archived data objects in the CANDELS catalog of Galametz et al. (2013). where the individual pointings are sufficiently deep and to look This catalog includes Spitzer IRAC fluxes of the WFC3 for serendipitously detected faint objects (Hatsukade et al. objects, extracted from the images of the Spitzer Extended 2013; Ono et al. 2014; Carniani et al. 2015; Fujimoto Deep Survey (SEDS; Ashby et al. 2013) at the positions of the et al. 2016; hereafter F16; Oteo et al. 2016). Another way is WFC3 sources (see Galametz et al. 2013 et al. for details).In to employ stacking analyses to obtain averaged mm/submm Section 3.3 we will show that the IRAC fluxes trace faint properties of high-redshift galaxies (e.g., Decarli et al. 2014; 1.1 mm emission better than the WFC3 fluxes, and therefore Scoville et al. 2014, D16). Here we take the second approach the majority of our analyses will be based on an additional and present stacking analyses of near-infrared (NIR) selected 3.6 μm selection in the CANDELS catalog. The 5 σ limiting galaxies in our ALMA 1.1 mm survey in the Subaru/XMM- magnitudes in our ALMA area for the FW160 and IRAC Newton Deep Survey Field (SXDF; Furusawa et al.